The invention relates to a switchable freewheeling two direction ratchet unit. The ratchet unit includes a coupling hub and coupling sleeve which, in the driving direction of rotation, are non-rotatingly connectable to each other via locking ratchets. The locking ratchets are held radially resiliently in first recesses of the first of the two coupling parts. The locking ratchets engage in recesses of the other coupling part, with the locking ratchets being disengagable from the recesses of the other coupling part via a control ring, control elements and a switching device. The control ring carries the control elements and is associated with a first coupling part so as to be pivotable to a limited extent. The control elements include first control faces on the locking ratchets. The control faces oppose each other and, depending on the position of the control ring, the control faces either contact each other or do not contact each other.
A freewheeling ratchet unit is known from U.S. patent Ser. No. 3,557,922. However, this freewheeling ratchet unit is suitable for rotation in only one direction.
DE 35 28 591 C2 illustrates a freewheeling unit with a coupling sleeve recess engaged by a locking ratchet in the torque transmitting position by a radially movable control pin with the locking ratchet being moved inwardly. During the relative movement of the coupling sleeve and coupling hub, the ratchet is pressed into contact with the bearing bore of the coupling sleeve by spring pressurizing it radially outwardly. This leads to increased wear.
It is the object of the present invention to propose a freewheeling ratchet unit which is suitable for the transmission of torque in two directions of rotation. In accordance with the invention, the first coupling part is associated with two sets of locking ratchets which, in the two opposed directions of rotation, are engaged with or disengaged from the recesses of the other coupling part. The control elements radially engage between two sets of associated locking ratchets and, for the purpose of operating the locking ratchets, include control faces pointing in opposite circumferential directions.
The advantage of this design is that when disengaged from the control elements, the locking ratchets are held in a lifted position vis-a-vis the coupling part rotating relative thereto. The respective locking ratchets are lifted as a function of the direction of rotation for one of the two torque transmitting directions. In addition, it is proposed that the locking ratchets, when disengaged from the control elements, should be held so as to be enclosed in the first recesses.
In a preferred embodiment, the control elements are designed to be mirror-symmetrical relative to radial axes of the sleeve and hub. Preferably, the coupling sleeve constitutes the first coupling part with the control faces of the control elements extending underneath the locking ratchets to associate the control elements, position the control ring as well as arrange the switching device.
Lifting of the ratchets is preferably achieved by the control faces of the control elements. The locking ratchets, in opposition to the driving direction of rotation, extend at a radially increasing distance relative to the axis of rotation. As the control ring and thus the control elements are held back for the purpose of being switched off relative to the driving coupling part, the control faces of the locking ratchets slide on the control elements in the direction opposite to the direction of rotation, with the locking ratchets being moved radially outwardly out of the locking recesses in the second coupling part, i.e. the coupling hub.
In order to achieve uniform disengagement of the locking ratchets, the control faces are arranged centrally relative to the locking ratchets and form part of a recess. However, the control faces may also be arranged laterally.
In a preferred embodiment, starting from the control ring, the control elements radially pass through an aperture in the first coupling part. The control elements, in their end positions in the circumferential direction, are supported on one of the two circumferential limiting faces of the apertures or the control ring abuts against stops at the coupling part relative to which it is movable. In this way, it is possible to do without guiding the control ring in a groove.
To facilitate assembly, the control elements are releasably connected to the control ring.
For controlling the control ring, it is proposed in a further embodiment of the invention that the first coupling part should be associated with ramp faces. The ramp faces provide a fixed stop or a switching device. Also, the control ring or the control elements include retaining lugs radially projecting beyond the contour of the control ring. Thus, depending on the direction of rotation, the retaining lugs will be stopped or released by the ramp faces.
The switching device for operating the control ring may be designed in different ways. Thus, the switching device may consist of a radially resilient journal constituting a stop or of a pivotable angle lever with a pair of stops. However, it is also possible for the control ring to be loaded by a braking device.
In order to achieve rigid coupling of the output unit in both directions of rotation, it is proposed in a further embodiment of the invention to move the control ring into a central position where the locking ratchets of the two sets of locking ratchets simultaneously engage in the recesses of the coupling part. For such a design of a freewheeling ratchet unit, in particular, there is provided a switching unit in the case of which a control sleeve includes a control slot intersecting the axis of rotation which is non-rotatingly, but axially movably associated with the first coupling part. A control pin radially projects from the control ring and is guided in the control sleeve and the control sleeve is axially movable, via a switching fork or a similar switching element, which is externally operated and engages a switching groove in the control sleeve.
From the following detailed description taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.